title: A density-functional study of the adsorption of methane-thiol on the (111) surfaces of the Ni-group metals: II. Vibrational spectroscopy.
abstract: The vibrational eigenstates of methane-thiol (CH(3)SH) and methane-thiolate (CH(3)S) in the gas phase and in dense monolayers adsorbed on the (111) surfaces of the Ni-group metals have been investigated within the framework of density-functional theory using generalized response and force-constant techniques. For isolated CH(3)SH good agreement of eigenfrequencies and intensities with the measured infrared spectra is achieved. For the CH(3)S radical, experimental information from laser-induced fluorescence spectroscopy is available only for selected eigenmodes. The theoretical predictions show reasonable agreement for the C-H deformation and C-S stretching modes, but predict much higher C-H stretching frequencies in better agreement with estimates based on the vibrational fine structure of the photoemission spectra. For methane-thiol monolayers on Ni(111) and Pt(111) the calculations predict stronger red-shifts of the S-H and C-S stretching modes than reported from high-resolution electron energy loss spectroscopy (HREELS) on condensed multilayers which average over the first layer adsorbed on the metal and further physisorbed molecular layers. For methane-thiolate monolayers the calculations predict modest blue-shifts of the C-H stretching and rocking modes and for the asymmetric C-H deformation modes. Red-shifts are predicted for the symmetric C-H deformation and for the C-S stretching modes. Reasonable agreement with HREELS is achieved. The increased differences between symmetric and asymmetric C-H stretching and deformation modes induced by the adsorption is a consequence of the strongly tilted adsorption geometries.
authors.affiliation: Fakultät für Physik and Center for Computational Materials Science, Universität Wien, Sensengasse 8/12, A-1090 Wien, Austria.
authors.forename: David
authors.initials: D
authors.lastname: Karhánek
authors.forename: Tomáš
authors.initials: T
authors.lastname: Bučko
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hafner
mesh_terms: D000327:Adsorption; D005609:Free Radicals / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D008670:Metals / Q000737:chemistry; D008956:Models, Chemical; D009532:Nickel / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry; D010984:Platinum / Q000737:chemistry; D013055:Spectrophotometry, Infrared / Q000379:methods*; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D005740:Gases; D008670:Metals; D013438:Sulfhydryl Compounds; C005231:methylmercaptan; D010984:Platinum; D010165:Palladium; D009532:Nickel